1. Field of the Invention
The present invention relates to an internal combustion engine control apparatus that performs air-fuel ratio control and exhaust gas recirculation (EGR) control and, more specifically, to an internal combustion engine control apparatus that performs control such that harmful components are reduced in the exhaust gas entering a catalyzer before the catalyzer is activated.
2. Description of Related Art
Various type of internal combustion engine control apparatuses are disclosed in, for example, Japanese patent application unexamined publication Nos. SHO 57-146041 and SHO 59-561.
Each of the apparatuses disclosed in those publications has an EGR valve provided for controlling communication between the exhaust system and the intake system. The apparatus according to the publication No. SHO 57-146041 keeps the EGR valve open from the start of engine operation until the catalyzer temperature reaches such a level as to activate the catalyzer, and closes the EGR valve when such a high temperature is reached. On the other hand, the apparatus according to the publication No. 59-561 keeps the EGR valve open for a predetermined length of time from the start of engine operation, and closes the EGR valve when the predetermined length of time elapses.
Each of the apparatuses is intended to reduce harmful components in the exhaust gas entering the catalyzer before it is activated, thus reducing the harmful components in the exhaust gas emission from the exhaust system.
The apparatuses also perform air-fuel ratio control based on the O.sub.2 concentration in exhaust gas detected by an O.sub.2 sensor provided in the exhaust system.
These conventional apparatuses have the following problems.
Although combustion of air-fuel mixture largely depends on temperature during a certain period of time from the start of engine operation, the conventional apparatuses do not change the flow of EGR introduced into the combustion chamber. Such EGR control may sometimes result in engine stall.
The O.sub.2 sensor does not properly function until the temperature of an O.sub.2 concentration detecting element reaches a predetermined level to activate the element. Therefore, appropriate air-fuel ratio control cannot be performed for a certain period of time from the start of engine operation until the O.sub.2 concentration detecting element is activated. Naturally, during such a period, harmful components in exhaust gas cannot be sufficiently reduced.